Vulcanizable compound



Patented July 23, 1935 UNITED STATES PATENT OFFICE VULCANIZABLE COMPOUNDAlvin N. Gray. Baltimore, It, and Archie I.

Kemp, Westwood, N. 1.. alcignora to Dell Telephone Laboratories, rated,New York, N. Y., a corporation of New York No Drawing. applicationAugust 11,

Original 1930, Serial No. 474,384. Divided till this],- plloaflonOctober 29, 1 Serial No. 40,240. In Canada July 21, 1981 9 Galina. (Cl.106-13) copending application Serial No. 474,364, filed August 11, 1930,entitled Insulated conductors.

In the manufacture of electrical conductors provided with an insulatedcovering of vulcanizable material it is common practice to extrude theinsulating material about the bare conductor which is then coiled in apan of soapstone or similar material to keep the turns of wire fromsticking together. The pans of wire thus coiled are then placed in avulcanizing chamber and subjected to heat and pressure untilvulcanization is completed, after which thecoils of insulated wire arecleaned and wound on supply reels. Such a process is objectionable notonly because of the labor expense involved in the panning operation andthe reeling after vulcanization, but also because of the time requiredand the tendency for the conducting core to become decentralized in itsinsulating sheath prior to vulcanization and for the insulating sheathto become distorted.

It is therefore an object of the present invention to provide aninsulated electrical conductor in which the conducting core issurrounded by a uniform layer of insulating material vulcanized thereonat high speed and with a minimum amount of handling.

To attain this object and in accordance with one feature of theinvention an insulating compound is provided which is capable ofextremely rapid vulcanization and yet one which, when mixed and appliedin accordance with the process defined, does not vulcanize during theextruding operation. Furthermore, this compound is so proportioned thatalthough it has sufiicient plasticity and is soft enough to permitextruding at high speed and at comparatively low temperatures, itnevertheless possesses sufilcient rigidity to prevent the conductingcore from becoming decentralized or the sheath distorted duringmanufacture.

To attain this object there is provided an insulating compound which isadapted to be extruded about an electrical conductor and to meet theexacting requirements of a continuous vulcanization process when carriedon at high speeds. This compound consists of the following ingredientsin substantially the proportions Per cent Smoked sheet rubber 22Reclaimed rubber (boot and shoe) 10 Reclaimed rubber (whole tire) 10Mineral rubber 5 whiting 44.7 Zinc-oxide 2.5 Anti-oxidant 1.5 Sulphur1.0 Softener (pine tar oil) 3.0 Ultra-accelerator .3

The reclaimed rubber is specified primarily for the sake of economy andthe percentage of such rubber to new rubber may be varied over a ratherwide range so long as the total vulcanizable rubber content of thecompound remains substantially 30%. The mineral rubber and pine tar oilwhich serve respectively as plasticizer and softener are present in suchproportions as to give the compound the necessary plasticity andsoftness to permit it being extruded at high speeds while maintained atarelatively low temperature such that prevulcanization does not occurand, on the other hand, to have sufficient rigidity to preclude anypossibility of decentralization of the core or distortion of the sheathbefore vulcanization. To further prevent decentralization of the coreand to permit extruding and vulcanizing continuously at a high rate ofspeed an ultraaccelerator is employed in an amount to bring aboutcomplete vulcanization in a fraction of a minute when employed under theconditions to be described. Preferably the amount of ultraacceleratorpresent is 1% or more of the total rubber content and in no case shouldit be less than 0.9%. The term "ultra-accelerator defines an acceleratorsuch as tetramethylthiurammonosulphide or tetramethylthiuramdisulphide,and the proportions of ultra-accelerator indicated above refer to theseparticular ultra-accelerators or ones having equivalent acceleratorpower. Accelerators of this type have not been used heretofore inquantities such as specified for the purpose of vulcanizing or coatingconductors and could not be so used in any process requiring panvulcanization since such compounds to resist distortion in panning mustbe stiffer and extruded at higher temperatures which would result inprevulcanlzing during mixing and extruding. The remaining ingredients ofthis compound are present for the same purpose as in common practice.The zinc-oxide activates the accelerator while the antioxidant resistsageing of the compound. Sulphur serves as the vulcanizing agent andwhiting is used solely as a filler and consequently may be replaced byother fillers in commercial use.

in preparing this compound, all of the materials except theultra-accelerator are masticated in a commercial type mixer and putthrough strainer. The compound is then allowed to cool for a period ofapproximately of an hour instead of ageing for 418 hours as is thecustomary practice. The ultra-accelerator is then added in the warmingrolls with just sufdcient working to thoroughly mix it and the compoundis used soon thereafter as possible, which should always be within aperiod of two hours.

This vulcanizing compound is preferably used ii'l. accordance with theprocess described in de tail in our United States Patent No. l,927,-=00,dated Sept. 19, 1933, in which case it may be fed into the extrudinghead either by hand or by an automatic device of the intermittent typearranged to stop feeding whenever suiidcient com= pound is in theextruding chamber. In order to prevent prevulcanization occurring in theextrud ing chamber, the head should be designed so that the compound isdirected from. the end of the extruding screw to an angular chamberaround. the wire eliminating all pockets in which the compound may standand become vulcanized before application to the wire. The temperature ofthe extruding head must be such as to give the com pound suificientplasticity without causing too rapid an action of ultra-accelerator.These conditions are satisfactorily met if the extruding head ismaintained at a temperature of approximately 160 F. which isconsiderably lower than used heretofore. This requirement is preferablymet by means of an automatic regulator by which the circulation of steamand water, respectively, heats and cools the extruding head to maintainthe desired temperature.

When using the compound in accordance with this invention for theinsulation of electrical conductors, a decidedly superior productresults. Not only is the core centralized with respect to the coveringbut the covering, per se, possesses superior mechanical and electricalproperties. As a result of the exceedingly rapid vulcanization therubber compound does not deteriorate to the extent that a similarcompound does when subjected to a slow'vulcanizing process. Furthermore,in producing this improved conductor the expense of handling, reeling,etc., inherent in pan vulcanizing methods, is eliminated; the process iscontinuous; and may be carried on at a high rate of speed limitedpractically only by the rate at which satisfactory extrusion ispossible. For example, in coating No. 17 B & S gauge drop wire with acoating 3/ 64 of an inch thick, satisfactory results are obtained whenthe speed of travel of the wire is from 400 to 500 feet per minute.Since these results were obtained when using a vulcanizing chamber feetin length, the corresponding vulcanizing periods for these speeds wouldbe 12 to 15 seconds. Such a period of vulcanization is exceedingly smallwhen compared with the vulcanizing periods used heretofore for thevulcanization of insulating compounds on electrical conductors andprevents to a considerable degree the deterloration which occurs in therubber when a corresponding compound is vulcanized at the rate commonlyemployed in practice.

The specific compound described is one which is particularly suitable asthe covering for drop wire. Obviously, in order to provide an insulatingsheath having different physical or electrical properties, or for otherreasons, certain of the constituents of this compound may be replaced byequivalents or employed in varying amounts without departing from thespirit of the invention as defined in the appended claims.

What is claimed is:

1. A vulcanizable insulating compound for coating electrical conductorscontaining rubber, plasticizer, softener and an ultra accelerator socompounded that the resulting compound is sud ficiently plastic and softat a temperature of F. to permit extrusion upon a conductor at the rateof 400 feet per minute without being su'Eiclently soft to permitdecentralization of the conductor when vulcanized at a temperaturecorresponding to to pounds steam pressure.

2. A vulcanizable insulating compound for coating electrical conductors,the physical properties oi said compound being such as to permit itsbeing extruded without vulcanization upon a conductor at the rate of 400feet per minute while maintained at a temperature of approximately 160F. and substantially completely vulcanized in 15 seconds while subjectedto a temperature corresponding to 170 to 175 pounds steam pres sure.

3. A vulcanizable insulating compound for coating electrical conductorscomprising the fol lowing ingredients in substantially the proper tionsnamed: crude rubber 22.0%, reclaimed rub= ber 20.0%, mineral rubber5.0%, whitin 4am,

zinc oxide 2.5%, anti-oxidant 1.5%, sulphur 1.0%, pine tar oil 3.0%,ultra-accelerator 3%.

4. A vulcanizable insulating compound for coating electrical conductorscontaining rubber, plasticizer, softener and an ultra-accelerator of thegroup consisting of tetramethyl-thiurammonosulphide andtetramethylthimam-disulphide so compounded that the resulting compoundis sufficiently plastic and soft at a temperature of 160 F. to permitextrusion upon a conductor at the rate of 400 feet per minute withoutbeing sufficiently soft to permit decentralization of the conductor whenvulcanized at a temperature corresponding to 1'70 to 175 pounds steampressure.

5. A vulcanizable insulating compoundfor coating electrical conductorscontaining rubber, plasticizer, softener andtetramethylthiurammonosulphide so compounded that the resulting compoundis sufiiciently plastic and soft at a temperature of 160 F. to permitextrusion upon a conductor at the rate of 400 feet per minute withoutbeing sufficiently soft to permit decentralization of the conductor whenvulcanized at a temperature corresponding to 170 to 175 pounds steampressure. v

6. A vulcanizable insulating compound for coating electrical conductorscontaining rubber, plasticizer, softener andtetramethylthiuramdlsulphide so compounded that the resulting compoundis sufliciently plastic and soft at a temperature of 160 F. to permitextrusion upon a conductor at the rate of 400 feet per minute withoutbeing sufilciently soft to permit decentralization of the conductor whenvulcanized at a temperature corresponding to 1'10 to 175 pounds steampressure.

'1. A vulcanizable insulating compound for coating electrical conductorscomprising the 101- lowing ingredients in substantially the proportionsnamed: crude rubber 22.0%, reclaimed rubber 20.0%, mineral rubber 5.0%,whiting 44.7%, zinc oxide 2.5%, anti-oxidant 1.5%, sulphur 1.0%, pinetar oil 3.0%, an ultra-accelerator of the group consisting oftetramethylthiurammonosulphide and tetramethylthiuramdisulphide .3%.

8. A vulcanizable insulating compound for coating electrical conductorscomprising the following ingredients in substantially the proportionsnamed: crude rubber 22.0%. reclaimed rubber 20.0%. mineral rubber 5.0%,whim 44.7%, zinc oxide 2.5%, anti-oxidant 1.5%, sulphur 1.0%, pine taroil 3.0%, tetramethylthiurammonosulphide .3%.

9. A vulcanizable insulating compoundv for coating electrical conductorscomprising the following ingredients in substantially the proportionsnamed: crude rubber 22.0%, reclaimed rubber 20.0%, mineral rubber 5.0%,whiting 44.7% zinc oxide 2.5%, anti-oxidant 1.5%, sulphur 1.0% pine tar011 3.0%, tetramethylthiuramdisuiphlde 3%.

. ALVIN N. GRAY.

ARCHIE R. KEMP.

